1. Field of the Invention
The invention relates generally to motion detectors, and more particularly to a motion and direction detector of a railway vehicle and in some applications on an end-of-train (EOT) railroad telemetry system.
2. Description of the Prior Art
In railway systems such as those employing locomotive drawn trains, it can sometimes be difficult for the engineer or other operator to reliably be apprised of the state of motion of one or more vehicles that are located remotely from him. For example, when starting a train from a stop position it can in some operations be particularly difficult for the train driver to know when the driving force of the locomotive has propagated through the interconnected cars and accelerated the last vehicle into motion. Conversely, when coming to a stop, it is difficult for the driver to know when the last car has been decelerated to a standstill. Knowledge of these conditions of motion of the last vehicle can be extremely useful to the driver in controlling operation of the train.
EOT signaling and monitoring equipment is now widely used in place of cabooses, to meet operating and safety requirements of railroads. The information monitored by the EOT unit typically includes air pressure of the brake pipe, battery condition, marker, light operation, and train movement. This information can be transmitted to the crew in the locomotive by a battery powered telemetry transmitter. In addition, the EOT unit typically includes a marker light mounted at a specific height above the track and having a well defined beam pattern.
The early EOT telemetry systems were one-way systems; that is, data was periodically transmitted from the EOT unit to Head of Train (HOT) unit in the locomotive where the information was displayed. More recently, two-way systems have been introduced wherein radio transmissions are also made by the HOT unit to the EOT unit.
With the continuing development of EOT units for use in two-way railroad telemetry systems, one goal has been to improve the functionality of the existing motion sensor, especially when operated on a smooth rail. In addition, some older types of sensors do not report direction of motion.
Many contemporary motion and direction detectors for EOT units commonly employ a piezoelectric film as the sensing element. Examples of such contemporary motion and direction sensors are disclosed in U.S. Pat. No. 5,376,925 to Crisafulli et al., U.S. Pat. No. 5,003,824 to Fukada et al. and U.S. Pat. No. 4,752,053 to Boetzkes. Crisafulli, Boetzkes and Fukada each disclose devices which have two sensors utilizing piezoelectric film. One piezoelectric sensor for detecting motion, and a separate piezoelectric sensor for detecting direction.
Although piezoelectric film has been the medium of choice in many contemporary sensors, there can be disadvantages associated with the use of piezoelectric films especially environmental conditions such as shock, breakage, susceptibility to EMI, and temperature. Additionally, the piezoelectric sensors of contemporary motion detectors can also take hours to calibrate.
Furthermore, contemporary motion detectors typically may keep all motion and direction monitoring electronics powered and operating continuously. This may force the designer to use very high impedance sensors and processing electronics which can in some designs lead to the problems of sensitivity to temperature and humidity and susceptibility to EMI. Complex and time consuming algorithms can then be required to account for the errors introduced by these conditions.
Moreover, motion and direction detecting devices disclosed in each of the above patents employ separate piezoelectric sensors for determining motion and direction.